ESR1 and breast cancer: We used MDA-MB-231, HS578T, BT549, SUM149, and HCC3153 as triple-negative (TN) breast cancer cell lines (estrogen receptor (ER)-negative, HER2-negative); SKBR3, HCC1569, and HCC1954 as HER2-positive cell lines (ER-negative, HER2-positive); MCF7 and T47D as a luminal A model (ER-positive, HER2-negative); and finally, BT474 as a luminal B example (ER- and HER2-positive).